Due to the development in radio communication technologies and the introduction of new radio communication services, there has been a desire to more effectively use a finite frequency resource. To enhance a frequency utilization efficiency, a spectrum efficiency optimization scheme through a performance optimization of a radio communication system and a scheme of minimizing interference with another radio communication system, and the like have been used. The performance optimization may be, for example, a multiple access scheme, an encoding technology, a modulation efficiency, an information compression technology, and the like.
In addition to the above schemes, a frequency sharing method is proposed to enhance a frequency utilization efficiency in a currently using frequency band such as a television (TV) band.